Zoltan Hudak
mbed API for Raspberry Pi boards.
mbedPi
This is an attempt to implement a limited number of mbed APIs for Raspberry Pi single-board computers. The project was inspired by and based on the arduPi library developed for the Arduino by Cooking Hacks .
Specifications
- Chip: Broadcom BCM2836 SoC
- Core architecture: Quad-core ARM Cortex-A7
- CPU frequency: 900 MHz
- GPU: Dual Core VideoCore IV® Multimedia Co-Processor
- Memory: 1GB LPDDR2
- Operating System: Boots from Micro SD card, running a version of the Linux operating system
- Power: Micro USB socket 5V, 2A
Connectors
- Ethernet: 10/100 BaseT Ethernet socket
- Video Output: HDMI (rev 1.3 & 1.4)
- Audio Output: 3.5mm jack, HDMI
- USB: 4 x USB 2.0 Connector
- GPIO Connector: 40-pin 2.54 mm (100 mil) expansion header: 2x20 strip providing 27 GPIO pins as well as +3.3 V, +5 V and GND supply lines
- Camera Connector: 15-pin MIPI Camera Serial Interface (CSI-2)
- JTAG: Not populated
- Display Connector: Display Serial Interface (DSI) 15 way flat flex cable connector with two data lanes and a clock lane
- Memory Card Slot: Micro SDIO
GPIO connector pinout
Information
Only the labels printed in blue/white or green/white (i.e. p3, gpio2 ...) must be used in your code. The other labels are given as information (alternate-functions, power pins, ...).
Building programs for the Raspberry Pi with mbedPi
I use Qt Creator for development, however you can use any other IDE available on the Raspberry Pi (e.g. Geany) if you like. For a quick try:
- Install Qt and the Qt Creator onto your Raspberry Pi. Then create a new "Blinky" Plain non-Qt C++ Project as follows:
- Change the main code as below:
main.cpp
#include "mbedPi.h"
int main()
{
DigitalOut myled(p7);
while(1) {
myled = 1; // LED is ON
wait(0.2); // 200 ms
myled = 0; // LED is OFF
wait(1.0); // 1 sec
printf("Blink\r\n");
}
}
- Copy the mbedPi.zip file into your project's folder and unzip.
- Add the mbedPi.h and mbedPi.cpp files to your project by right clicking on the "Blinky" project and then clicking on the "Add Existing Files..." option in the local menu:
- Double click on Blinky.pro to open it for editing and add new libraries by inserting a new line as follows:
- Compile the project.
- Connect an LED through a 1k resistor to pin 7 and the ground on the Raspberry Pi GPIO connector.
- Run the binary as sudo (sudo ./Blinky) and you should see the LED blinking.
- Press Ctrl+c to stop running the application.
Diff: source/gpio.cpp
- Revision:
- 1:1f2d9982fa8c
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/source/gpio.cpp Tue Dec 20 12:08:07 2022 +0000
@@ -0,0 +1,145 @@
+#include "mbed.h"
+
+extern struct bcm2835_peripheral gpio;
+
+/********** FUNCTIONS OUTSIDE CLASSES **********/
+
+// Write a HIGH or a LOW value to a digital pin
+void gpio_write(PinName pin, int value)
+{
+ if (value == HIGH)
+ GPSET0 = (1 << pin);
+ else
+ if (value == LOW)
+ GPCLR0 = (1 << pin);
+
+ wait_us(1); // Delay to allow any change in state to be reflected in the LEVn, register bit.
+}
+
+// Reads the value from a specified digital pin, either HIGH or LOW.
+int gpio_read(PinName pin)
+{
+ Digivalue value;
+ if (GPLEV0 & (1 << pin))
+ value = HIGH;
+ else
+ value = LOW;
+
+ return value;
+}
+
+// Function select
+// pin is a BCM2835 GPIO pin number NOT RPi pin number
+// There are 6 control registers, each control the functions of a block
+// of 10 pins.
+// Each control register has 10 sets of 3 bits per GPIO pin:
+//
+// 000 = GPIO Pin X is an input
+// 001 = GPIO Pin X is an output
+// 100 = GPIO Pin X takes alternate function 0
+// 101 = GPIO Pin X takes alternate function 1
+// 110 = GPIO Pin X takes alternate function 2
+// 111 = GPIO Pin X takes alternate function 3
+// 011 = GPIO Pin X takes alternate function 4
+// 010 = GPIO Pin X takes alternate function 5
+//
+// So the 3 bits for port X are:
+
+// X / 10 + ((X % 10) * 3)
+
+void bcm2835_gpio_fsel(uint8_t pin, uint8_t mode)
+{
+ // Function selects are 10 pins per 32 bit word, 3 bits per pin
+ volatile uint32_t* paddr = (volatile uint32_t*)gpio.map + BCM2835_GPFSEL0 / 4 + (pin / 10);
+ uint8_t shift = (pin % 10) * 3;
+ uint32_t mask = BCM2835_GPIO_FSEL_MASK << shift;
+ uint32_t value = mode << shift;
+
+ bcm2835_peri_set_bits(paddr, value, mask);
+}
+
+/**
+ * @brief
+ * @note
+ * @param
+ * @retval
+ */
+void gpio_dir(PinName pin, PinDirection direction)
+{
+ uint8_t gpfsel = pin / 10;
+ uint8_t shift = (pin % 10) * 3;
+ uint32_t mask = BCM2835_GPIO_FSEL_MASK << shift;
+ uint32_t outp = BCM2835_GPIO_FSEL_OUTP << shift;
+
+ if (direction == PIN_OUTPUT) {
+ *(gpio.addr + gpfsel) &= ~mask;
+ *(gpio.addr + gpfsel) |= outp;
+ }
+ else
+ if (direction == PIN_INPUT) {
+ *(gpio.addr + gpfsel) &= ~mask;
+ }
+}
+
+/**
+ * @brief
+ * @note
+ * @param
+ * @retval
+ */
+void gpio_mode(PinName pin, PinMode mode)
+{
+ mode == PullUp ? gpio_write(pin, HIGH) : gpio_write(pin, LOW);
+}
+
+/**
+ * @brief
+ * @note
+ * @param
+ * @retval
+ */
+uint8_t shiftIn(PinName dPin, PinName cPin, bcm2835SPIBitOrder order)
+{
+ uint8_t value = 0;
+ int8_t i;
+
+ if (order == MSBFIRST)
+ for (i = 7; i >= 0; --i) {
+ gpio_write(cPin, HIGH);
+ value |= gpio_read(dPin) << i;
+ gpio_write(cPin, LOW);
+ }
+ else
+ for (i = 0; i < 8; ++i) {
+ gpio_write(cPin, HIGH);
+ value |= gpio_read(dPin) << i;
+ gpio_write(cPin, LOW);
+ }
+
+ return value;
+}
+
+/**
+ * @brief
+ * @note
+ * @param
+ * @retval
+ */
+void shiftOut(PinName dPin, PinName cPin, bcm2835SPIBitOrder order, uint8_t val)
+{
+ int8_t i;
+
+ if (order == MSBFIRST)
+ for (i = 7; i >= 0; --i) {
+ gpio_write(dPin, val & (1 << i));
+ gpio_write(cPin, HIGH);
+ gpio_write(cPin, LOW);
+ }
+ else
+ for (i = 0; i < 8; ++i) {
+ gpio_write(dPin, val & (1 << i));
+ gpio_write(cPin, HIGH);
+ gpio_write(cPin, LOW);
+ }
+}
+